title: Bridging the gap between clinical failure and laboratory fracture strength tests using a fractographic approach.
abstract: OBJECTIVE
  The aim of this study was to analyze and to compare the fracture type and the stress at failure of clinically fractured zirconia-based all ceramic restorations with that of morphologically similar replicas tested in a laboratory setup.
  
  
  METHODS
  Replicas of the same shape and dimensions were made for 19 crowns and 17 fixed partial dentures, all made of veneered zirconia frameworks, which fractured during intra-oral service. The replicas were statically loaded by applying axial load in a universal testing machine. The principles of fractography were used to identify the location and the dimensions of the critical crack and to estimate the stress at failure. Failure was classified according to origin and type (P<0.05 was considered significant).
  
  
  RESULTS
  Clinically fractured restorations failed due to either: delamination of the veneer ceramic (28.2+/-9MPa), defects at core veneer interface (27.7+/-6MPa), the generation of Hoop stresses (884.3+/-266MPa), radial cracking (831MPa), or fracture of the connector (971+/-343MPa). The replicas failed by mainly by cone cracking of the veneer ceramic (52.4+/-34.8MPa) or by fracture of the connector (1098.9+/-259MPa). The estimated stress at failure was significantly higher for the replicas compared to the clinically fractured restorations (F=6.8, P<0.01).
  
  
  CONCLUSIONS
  Within limitations of this study, careful design of fracture strength test would lead to more clinically relevant data. The performance of zirconia veneered restorations could be further improved with careful design considerations.
authors.affiliation: Department of Dental Materials Science, Academic Center for Dentistry Amsterdam (ACTA), Universiteit van Amsterdam and Vrije Universiteit, The Netherlands. mabou@acta.nl
authors.forename: Moustafa N
authors.initials: MN
authors.lastname: Aboushelib
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Feilzer
authors.forename: Cees J
authors.initials: CJ
authors.lastname: Kleverlaan
mesh_terms: D000465:Algorithms; D003442:Crowns; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000295:instrumentation; D003801:Dental Veneers; D003779:Denture Design; D003830:Denture, Partial, Fixed; D055119:Elastic Modulus; D006244:Hardness; D006801:Humans; D007754:Laboratories, Dental; D008422:Materials Testing / Q000379:methods; D008855:Microscopy, Electron, Scanning; D013314:Stress, Mechanical; D013499:Surface Properties; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003764:Dental Materials; D003776:Dental Porcelain; D015040:Zirconium; C028541:zirconium oxide